On cross-validation and resampling of BRDF data measurements

Abstract

ceiling floortile pinkwall walkway painted agglomerate granite polished ceramic plastic with a glossy varnish Figure 1: Four material samples as the subject of the validation. The samples are referred by their location in a building. AbstractWe discuss the validation of BTF data measurements by means used for BRDF measurements. First, we show how to apply the Helmholtz reciprocity and isotropy for a single data set. Second, we discuss a cross-validation for BRDF measurement data obtained from two different measurement setups, where the measurements are not calibrated or the level of accuracy is not known. We show the practical problems encountered and the solutions we have used to validate physical setup for four material samples. We describe a novel coordinate system suitable for resampling the BRDF data from one data set to another data set. Further, we show how the perceptually uniform color space CIE 1976 L * a * b * is used for crosscomparison of BRDF data measurements, which were not calibrated.

Lightdrum—Portable Light Stage for Accurate BTF Measurement on Site

“…The methodology for comparison of two BTF datasets measured with different instruments has not yet been developed and published and it is more involved problem than for BRDF gantries (such as the method in [39]). It seems to be an interesting topic for further research.…”

Dynamic bidirectional reflectance distribution functions: Measurement and representation

“…Reflection measurements are normally made using gonioreflectometers ͑also called scatterometers͒, which measure the reflected light for a single incident and reflected angle combination at a time. [2][3][4][5][6][7][8] Minutes to hours are typically required for sufficient measurements to properly characterize the BRDF of a material at a given wavelength. Because of the long measurement times involved, this technique is obviously inapplicable to the situation where the surface properties are rapidly changing.…”

Accordance of Light Scattering from Design and De-Facto Variants of a Daylight Redirecting Component

“…It provided an error estimate for the comparison but was limited in directional resolution [17]. Similar setups have further been used to compare scattering models with measurements and to cross-validate BSDF data [18][19][20]. In the previous work it was partly necessary to resample the directional data for comparison as the data sources differed in directional resolution, the instrument's properties where unknown or the simulation environment limits the options.…”